UNLABELLED:Simultaneous liver and kidney transplantation (SLKT) remains the procedure of choice for patients with both endstage liver disease and kidney failure. Stringent guidelines are needed to avoid unnecessary kidney transplantation. A recent consensus meeting proposed criteria based on the Modified Diet in Renal Disease (MDRD)-6 equation to estimate glomerular filtration rate (GFR). The aims of this study were to compare GFR equations to true GFR in candidates for liver transplantation (LT) and to determine the impact of inaccuracies on the current guidelines for SLKT. Three hundred stable cirrhosis patients evaluated for LT were studied. All patients had iohexol clearance to measure GFR at evaluation under stable conditions. Measured GFR (mGFR) was compared to MDRD-4, MDRD-6, and Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equations. MDRD-6 was the most accurate equation to predict GFR. In the 290 patients with mGFR >30 mL/min/1.73 m(2), 15 patients (7%) had estimated GFR (eGFR) ≤40 mL/min/1.73 m(2) based on the MDRD-6 equation, defining "discordant" patients. Among them, two underwent SLKT and 13 underwent LT alone. None of those who survived more than 1 year after LT alone (n = 8) developed renal dysfunction thereafter. In multivariate analysis, discordant patients were older (P = 0.03) and had lower sodium level (P = 0.02). CONCLUSION:The MDRD-6 equation was superior to other equations at identifying cirrhosis patients with true GFR <30 mL/min/1.73 m(2). However, the MDRD-6 equation also tended to underestimate renal function in a subgroup of patients with true GFR >30 mL/min/1.73 m(2), with a potential risk of unnecessary kidney transplantation if applying current U.S. recommendations for SLKT.